1. Field of the Invention
The present invention relates to lids for sanitary containers, such as those used to ship and store bulk pharmaceuticals. More particularly, the present invention relates to lid structures that contain venting ports to prevent the lids from becoming vapor locked on the container they cover.
2. Description of the Prior Art
In the manufacture and processing of pharmaceutical products, dairy products and other materials that require a sanitary processing environment, it is common for materials to be transported, stored and processed in stainless steel containers. The stainless steel containers are covered with lids that are joined to the container with a clamp. The containers, the lids and the clamps are typically made from stainless steel so that all components can be sanitized in an autoclave prior to use. In this manner, the container, lid and clamp can be kept sterile so as not to introduce harmful contamination into the pharmaceutical product being transported or stored.
When a pharmaceutical is placed in a container, the pharmaceutical is at a certain temperature and embodies a certain vapor pressure at that temperature. When the container is again opened at some later time, the temperature of the pharmaceutical may have changed. If the pharmaceutical stored in the container has cooled, its corresponding vapor pressure has also dropped within the container. Accordingly, the pressure within the container may be significantly lower than that of the surrounding ambient pressure. In such cases, the lid of the container is held in position by the pressure differential between the interior of the container and the air surrounding the container. Often, the lid pressure differential is so great that the lid of the container cannot be removed by hand. In such circumstances, the lid is said to be vapor locked. A tool, such as a screw driver, must then be used to pry the lid off of the container. This is often difficult to do without spilling or contaminating the stored pharmaceutical.
In other situations, pharmaceuticals are stored at cold temperatures or are stored in pools of liquified gas, such as liquid nitrogen. As the contents of the container increase in temperature, the vapor pressure within the container increases dramatically. In certain circumstances, the increase in pressure within the container is sufficient to dislodge the clamp around the lid or deform the container walls until the seal with the lid is breached.
An obvious solution to prevent pressure differentials within a container is to vent the container to ambient pressure. However, to vent a container is to provide an avenue for contaminants to enter the container and for pharmaceuticals to exit the container. Expensive one-way flow valves can be used to vent containers. However, the use of flow valves is impractical because such structures harbor contaminants and cannot be economically cleaned. As such, after each use, many prior art flow valve mechanisms are replaced.
A need therefore exists for a container venting system that vents a container to ambient pressure, yet prevents contamination within the container and prevents spillage from the container. The venting system must also be easily sanitized using traditional autoclaving techniques. This need is met by the present invention as it is described and claimed below.
The present invention is a venting system for a container and the overall container assembly that uses the venting system. A container and a lid are provided. The lid of the container defines a venting port for equalizing gas pressure within the container. A support platform is placed over the venting port. The support platform defines a plurality of holes. Placed in each of the holes is a filter element. The filter element is made of a porous sintered powder metal having a pore size of no greater than five microns. In this manner the filter elements enable gas to vent to and from the container, yet the contents of the container are prevented from passing through the filter elements should the contents of the container touch the filter elements.
The filter elements, support platform and container lid are all made of the same metal. In this manner, the components respond to temperature changes in the same manner. Furthermore, filter elements, support platform and container lid are capable of being sterilized together in the same industrial autoclave facility.